The present invention relates to data center infrastructure and operation, and more particularly, this invention relates to enabling an extension of Virtual Link Aggregation (vLAG+) in a Transparent Interconnection of Lots of Links (TRILL)-based fabric network.
TRILL is a Layer-2 (L2) protocol which provides the ability to build a scalable Local Area Network (LAN) that is capable of replacing conventionally-used spanning-tree and other protocols. Details of the solution are described as part of the Internet Engineering Task Force (IETF) TRILL working group, found at http://datatracker.ietf.org/wg/trill/. A collection of entities called Routing Bridges (RBs) implement the TRILL protocol. RBs enhance some existing 802.1 bridges to function in a transparent manner. These RBs may either interoperate with or replace the functions of any existing 802.1 bridges.
In existing 802.1 bridge deployments, vLAG is a very popular LAG solution that allows a host, switch, or some other device to connect itself to two different 802.1 upstream bridges. The two upstream bridges work together to present a single LAG port instance so that the downstream devices do not perform any special tasks for the LAG to exist. The downstream devices work as though they are connected to two ports of a single bridge. In order to support this functionality, the two upstream bridges are connected through a link referred to as an Inter Switch Link (ISL). These two physical upstream bridges exchange information through the ISL. This solution supports an active-active scheme for all the VLANs carried on any LAG port.
However, when an existing 801.q bridge function is enhanced or replaced by a RB function, there are issues that occur that are not capable of being handled with conventional schemes that threaten to destroy the existing behavior of vLAG. The main issue is that when two RBs detect one another, one of the RBs asserts the Appointer Forwarder role. This mechanism elects only one of the RBs to be able to forward traffic for a given VLAN. This is not a desirable outcome because the active-active load balancing scheme for any given VLAN is broken when only one RB is forwarding all traffic. Load balancing is one of the main advantages of having vLAG span across multiple 801.q bridges, and with conventional techniques, it is not possible to take advantage of this load balancing.